Collapsible and self-expanding cannula for a percutaneous heart pump and method of manufacturing

ABSTRACT

An expandable cannula for a percutaneous heart pump includes a substantially open proximal end and a substantially open distal end. The expandable cannula includes an elongate central portion disposed between the proximal end and the distal end, the elongate central portion having an inner surface and an opposing outer surface. A first fluid impermeable film is disposed on at least one of the inner surface and the outer surface. The first fluid impermeable film comprises a polymer and has a thickness within a range of from 10 μm to 200 μm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No.16/296,592, filed Mar. 8, 2019, which claims priority to provisionalapplication Ser. No. 62/647,883, filed Mar. 26, 2018, each of which isincorporated herein in by reference in their entireties.

BACKGROUND OF THE DISCLOSURE a. Field of the Disclosure

The present disclosure relates generally to percutaneous heart pumpsincluding a collapsible and self-expanding cannula fabricated from ashape memory alloy, such as nitinol. More specifically, the presentdisclosure relates to a collapsible and self-expanding cannula thatincludes an open proximal end, an open distal end, and an elongatefluid-impermissible wall structure formed from an inner balloon layer, acannula strut and an outer balloon layer that are thermally fused intoan integrated hybrid cannula structure, and methods of manufacturing thesame.

b. Background Art

Heart disease is a major health problem that claims many lives per year.After a heart attack or other major cardiac event, only a small numberof patients can be treated with medicines or other non-invasivetreatment. A significant number of patients, however, can recover from aheart attack or other cardiac event if provided with mechanicalcirculatory support in timely manner.

In one conventional approach for treating patients, a blood pump theleft ventricle of the heart and the aortic arch, to assist the pumpingfunction of the heart. Other known conventional applications involveproviding for pumping venous blood from the right ventricle to thepulmonary artery for support of the right side of the heart. The objectof the surgically inserted pump is to reduce the load on the heartmuscle for a period of time allowing the affected heart muscle torecover and heal. In some cases, surgical insertion may potentiallycause additional stresses in heart failure patients.

In many cases, percutaneous insertion of a left ventricular assistdevice (“LVAD”), a right ventricular assist device (“RVAD”), or in somecases a system for both sides of the heart (sometimes called biVAD) is adesirable alternative. To allow for percutaneous insertion, the pumpcomponent of the device is collapsible with self-expandability andincludes an impeller encased in a cannula, while blood, driven by theimpeller, traverses the interior of the cannula.

During insertion and use of the percutaneous heart pump, it is desirablethat the lubricity and integrity of the surfaces of the pump that areexposed to the patient vasculature be maximized. This maximization ofthe lubricity and integrity reduces the potential for blood hemolysisand irritation at the intravascular location of the pump. Improving thelubricity of the surfaces in such devices that interact with thevasculature of a patient (e.g., the blood or the blood vessels) willimprove their effectiveness and further improve patient outcomes.

SUMMARY OF THE DISCLOSURE

In one embodiment the present disclosure relates to a collapsible andself-expanding cannula for a percutaneous heart pump. The collapsibleand self-expanding cannula comprises: (i) an open proximal end; (ii) anopen distal end; and (iii) an elongate, fluid impermissible wallstructure. The elongate, fluid impermissible wall structure comprises:(a) a first balloon film disposed on an interior surface of the wallstructure and defining a first wall structure circumferential surface;(b) a second balloon film disposed on an exterior surface of the wallstructure and defining a second wall structure circumferential surface;and (c) a cannula strut disposed between the first balloon film and thesecond balloon film.

In another embodiment the present disclosure is directed to a method ofmanufacturing a collapsible and self-expanding cannula for apercutaneous heart pump. The method comprises: introducing a firstballoon film onto a supporting mandrel; expanding a cannula strut;introducing the expanded cannula strut onto the supporting mandrel suchthat the expanded cannula strut contacts and fits against the firstballoon film; introducing a second balloon film onto the supportingmandrel such that the second balloon film contacts and fits against theexpanded cannula strut; introducing a shrink tube onto the supportingmandrel such that the shrink tube contacts and fits against the secondballoon film and wraps around a surface of the second balloon filmthereby creating a balloon-strut-balloon assembly; heating theballoon-strut-balloon assembly so that at least one of the first balloonfilm and the second balloon film at least partially melts and at leastpartially adheres to the expanded cannula strut such that spaces withinthe balloon-strut-balloon assembly are filled up by polymer melt underan inward radial pressure exerted by the shrink tube thereby creating afused balloon film; and removing the shrink tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a heart pump configured forpercutaneous application and operation.

FIG. 2 is a plan view of one embodiment of a catheter delivery assemblyadapted to be used with a percutaneous heart pump.

FIG. 3 is one embodiment of an impeller assembly in a percutaneous heartpump.

FIG. 4 illustrates one embodiment of a collapsible and self-expandablecannula including a first balloon film, a cannula strut and a secondballoon film.

FIG. 5 is a cross-sectional view of the collapsible and self-expandablecannula of FIG. 4.

FIGS. 6A, 6B, and 6C illustrate various embodiments of a collapsible andself-expandable cannula including a strut, a first balloon film and asecond balloon film where each film comprises various polymer layers.

FIGS. 7A and 7B represent a flow diagram illustrating one embodiment ofa method to manufacture a collapsible and self-expandable cannula.

FIGS. 8A, 8B, 8C, 8D and 8E illustrate a supporting mandrel in which afirst balloon film, a cannula strut and a second balloon film have beenintroduced: 8A illustrates the smooth supporting mandrel coated withpolytetrafluoroethylene material providing the free release of thepolymer material from the coated surface; 8B illustrates the supportingmandrel with the first balloon film introduced; 8C illustrates thesupporting mandrel with the first balloon and the cannula strut; 8Dillustrates the balloon-strut-balloon assembly comprising a firstballoon film, a cannula strut and a second balloon film; and 8Eillustrates the balloon-strut-balloon assembly encapsulated by a shrinktube and the inward radial pressure exerted thereby on theballoon-strut-balloon assembly.

FIGS. 9A and 9B illustrate a blow molding device comprising a thermalmodule, a blow mold, and a blowing mandrel mounted on a movablecartridge and having a gas inlet. Shown is one embodiment before blowing(FIG. 9A) and after blowing (FIG. 9B).

FIG. 10 is a graph illustrating the austenite-martensite transition of atypical shape memory alloy.

DETAILED DESCRIPTION OF THE DISCLOSURE

Percutaneous heart pumps are generally designed to provide circulatorysupport for a patient suffering from a cardiac deficiency. Support canbe short term or long term, depending on the nature of the deficiency. Atypical percutaneous heart pump includes at least an inner sheath, anouter sheath, an impeller-type pump disposed distally on the innersheath, an external motor, a control console and other accessories. Whenthe device is deployed in the human anatomy, the inner sheath isrelatively stationary, while the outer sheath, with respect to the innersheath, is axially moveable. The pump unit is disposed along the distalportion of the inner sheath and comprises an impeller and a cannula. Thecannula is foldable and/or collapsible based on forces exerted upon itby the outer sheath; as such, the cannula is generally self-expanding.The collapsed profile, also commonly referred to as the low insertion(or stored) profile, is where the cannula is radially compressed due tothe compressive force exerted upon it by the outer sheath. When theouter sheath is slidably removed, the self-expanding cannula expands toits operating (or pumping) profile. This expansion is due to thesuperelastic polymers and shape memory alloys that are used to fabricatethe cannula. Although a number of embodiments of the present disclosureare described herein including a self-expanding cannula, one skilled inthe art will appreciate that other embodiments, such as where thecannula is not self-expanding, are also within the scope of the presentdisclosure.

It is generally desirable for the outer sheath as described herein toeasily slide off of the self-expanding cannula in order for thepercutaneous heart pump to operate effectively and efficiently. If thesurfaces between the cannula and the outer sheath stick together orcatch, it may potentially reduce the overall integrity of one or bothsurfaces. The process is reversed when the pump is removed from thepatient. The outer sheath slides over and collapses the cannula therebyreducing its profile and easing removal. The present disclosure providesan improved collapsible and self-expanding cannula for use incombination with a percutaneous heart pump that is fabricated in amanner that provides excellent lubricity of the collapsible andself-expanding cannula's surfaces and reduces the likelihood of damageor degradation during unsheathing and resheathing operations.

The improved collapsible and self-expanding cannula as disclosed hereinexhibits improved lubricity and overall performance through the use ofspecific materials from which the collapsible and self-expanding cannulais fabricated and by the manner in which fabrication is done. Thecollapsible and self-expanding cannula of the present disclosuregenerally is a hybrid composite structure comprising three components: afirst (inner) balloon film, a cannula strut (also called a stent) formedfrom a shape memory alloy, and a second (outer) balloon film. The firstand second balloon films may independently comprise one or a pluralityof polymer-based layers. Once suitably positioned, these threecomponents (i.e., the first and second balloon films and the cannulastrut) are at least partially thermally fused and integrated together tocreate an integrated cannula with a wall structure that has asubstantially smooth, continuous inner or interior surface and asubstantially smooth, continuous outer or exterior surface to facilitateuse in the percutaneous heart pump. Substantially smooth generally meansthat the surface does not impede or otherwise obstruct the flow of bloodthrough the lumen of the collapsible and self-expanding cannula orresist the advancement or retraction of the heart pump in the catheterassembly. By way of illustration and not limitation, a substantiallysmooth surface would feel generally smooth to the touch.

As used herein, the collapsible and self-expandable cannula isalternatively referred to as the “self-expanding cannula” or, simply,the “cannula”. In all aspects herein, these terms are usedinterchangeably and refer to the same structure. In contrast, the“cannula strut” refers to one of the components used to make theself-expandable and collapsible cannula, and, in many embodiments,comprises the shape memory alloy (e.g., nitinol) which imparts thesuperelasticity and shape memory that permits the cannula to collapseand return to its expanded configuration.

a. Heart Pump System Overview

Referring now to the Figures, and specifically to FIG. 1, there isillustrated one embodiment of a heart pump 10 that includes a catheterassembly 100 having a proximal end 104 adapted to connect to a motor 14and a distal end 108 (as shown in FIG. 2) adapted to be insertedpercutaneously into a patient (not shown in FIG. 1). Motor 14 isconnected by a signal line 18 to a control module 22 that provides powerand/or control signals to motor 14. Heart pump 10 may have an infusionsystem 26 and a patient monitoring system 30.

Infusion system 26 can provide a number of benefits to heart pump 10. Inone embodiment, infusion system 26 includes a source of infusant 34, afluid conduit 38 extending from infusant source 34 to proximal end 104of catheter assembly 100 and a fluid conduit 42 extending from proximalend 104 of catheter assembly 100 to a waste container 46. The flow of aninfusant to and from catheter assembly 100 can be by any means,including a gravity system or one or more pumps. In FIG. 1, infusantsource 34 includes an elevated container 50, which may be saline oranother infusant as necessary based on patient requirements. Flow fromelevated container 50 can be regulated by a pressure cuff 54 to elevatethe pressure of the fluid in container 50 to increase flow or by a pinchvalve 58 or by other means.

With continuing reference to FIG. 1, patient monitoring system 30 can beused to monitor the operation of the patient and/or pump 10. Forexample, patient monitoring system 30 can include a user interface 60coupled with a source of data 64. Data source 64 can include one or morepatient condition sensors, such as pressure sensors 68 that are inpressure communication with the patient and/or operating componentswithin the patient. In one embodiment, pressure sensors 68 fluidlycommunicate by a conduit 72 that extends between the sensors and aproximal portion of catheter assembly 100. Conduit 72 can include aplurality of separable segments and can include a valve 76 to enable ordisable the pressure communication to sensors 68.

Heart pump 10 is adapted to provide an acute or other short-termtreatment. A short-term treatment can be for less than a day or up toseveral days or weeks in some cases. With certain configurations heartpump 10 can be used for a month or more.

FIG. 2 illustrates one embodiment of catheter assembly 100 to be usedwith heart pump 10 (see FIG. 1). An impeller assembly 116 disposed atdistal end 108 of catheter assembly 100 is configured to pump bloodproximally or distally through or along a portion of heart pump 10 (seeFIG. 1) to convey blood from one body cavity to another. Impellerassembly 116 can be arranged to pump blood distally, such as in a rightheart assist mode to move blood from the right ventricle to thepulmonary artery. Proximal flow is optimal for left heart support tomove blood from the left ventricle to the aorta. Heart pump 10 (seeFIG. 1) can be used to treat patients with acute heart failure, STelevation myocardial infarction (STEMI), cardiac arrest, cardiacarrhythmia or other heart maladies as noted above. Heart pump 10 (seeFIG. 1) also can be used in connection with a surgical treatment tosupport the patient without providing full cardiovascular bypass. Apatient could be supported on the device for longer term with propercontrols and design.

One feature that facilitates percutaneous insertion is providingcatheter assembly 100 with a low profile configuration. For example,distal end 108 of catheter assembly 100 can be configured to have aboutan 11 French (approximately 3.5 mm) size in a first configuration forinsertion and an expanded configuration, such as up to about 21 French(approximately 7 mm) once in place in the body. The larger sizefacilitates greater flow rates by impeller assembly 116. Of course,other sizes for insertion and expansion configurations are within thescope of the present disclosure.

Catheter assembly 100 is configured to enable distal end 108 to reach aheart chamber after being inserted initially into a peripheral vessel.For example, catheter assembly 100 can have a suitable length to reachthe left ventricle and sufficient pushability and torquability totraverse the intervening vasculature. Catheter assembly 100 may includea multilumen catheter body 120 that is arranged to facilitate deliveryand operation of an impeller (see FIG. 3) of impeller assembly 116.Multilumen catheter body 120 includes outer sheath assembly 121 andinner sheath assembly 170. Further details concerning variousembodiments of multilumen catheter body 120 are described in more detailin U.S. Pat. No. 8,597,170.

A drive system is provided to drive an impeller within impeller assembly116. The drive system includes motor 14 and a drive controller, whichcan be integrated into control module 22 (see FIG. 1). Although motor 14may be configured to be disposed outside the patient, some structuresand assemblies described herein could be incorporated into a system inwhich a motor is miniaturized sufficiently to be inserted into thepatient in use, including into the vasculature.

A torque coupling system is provided for transferring torque from motor14 to impeller assembly 116. The torque coupling system is discussedfurther in U.S. Pat. No. 8,597,170, but in general can include amechanical or magnetic interface disposed between the motor 14 and driveassembly 146 that is disposed at proximal end 104 of catheter assembly100. The drive assembly 146 is coupled with the proximal end of innersheath assembly 170 and provides an elongate drive cable 148 extendingfrom the drive assembly 146, via center lumen of inner sheath assembly170, to the impeller shaft (see FIG. 3) of impeller assembly 116 wherethe drive cable 148 is securely affixed onto, or coupled with, animpeller shaft (see FIG. 3) or an impeller assembly 116. Thus, motor 14is coupled with a drive assembly 146 and directly drives the impeller tospin inside a cannula assembly 202 (which comprises a self-expandingcannula 300 and a flexible atraumatic tip 182) with self-expandingcannula 300 being affixed to the distal end of multilumen catheter body120 at inner sheath assembly 170. In the embodiment shown in FIG. 2,self-expanding cannula 300 comprises an open proximal end 183 and anopen distal end 184. Further, as described in detail below, in someembodiments, self-expanding cannula 300 includes an elongatefluid-impermissible (i.e., impermeable) wall structure 159 (see FIG. 3)where an impeller 165 coupled with the drive cable 148 is disposed.Other embodiments, where elongate wall structure 159 is not completelyfluid-impermissible are also within the scope of the present disclosure.

FIG. 2 also shows an infusion inflow assembly 150 that can form a partof infusion system 26 (see FIG. 1). The infusion in flow assembly 150 isprovided adjacent proximal end 104 in one embodiment. Infusion system 26(see FIG. 1) is configured to convey one or more fluids therein inconnection with operation of impeller assembly 116 or the conducting ofthe treatment. In one embodiment, an infusant, e.g., a medication or alubricating fluid, such as saline or other beneficial medium, isconveyed distally along the pump, e.g., within multilumen catheter body120, toward the operating components adjacent to distal end 108. Theinfusant can include lubrication fluids such as glucose or otherbiocompatible lubricants. Infusion inflow assembly 150 includes anextension tube 154 having a luer or other suitable connector 158disposed at a proximal end thereof and an inflow port in fluidcommunication with one or more lumens within catheter assembly 100. Alumen extending through extension tube 154 is adapted to be fluidlycoupled with a fluid source connected to connector 158, to deliver thefluid into catheter assembly 100 through one or more flow paths.

FIG. 3 illustrates one embodiment of cannula assembly 202 that may bedisposed and affixed near the distal end of inner sheath assembly 170(shown in FIG. 2). Self-expanding cannula 300 of cannula assembly 202houses impeller 165. Self-expanding cannula 300 comprises afluid-impermissible elongate wall structure 159 having an interiorsurface 161 and an exterior surface 163. In some aspects, the clearancebetween interior surface 161 of self-expanding cannula 300 and animpeller 165 is minimal to prevent harmful interactions therebetweenduring operation. Impeller 165 is carefully placed within self-expandingcannula 300 and journaled to inner sheath assembly 170 such thatimpeller 165, as driven by drive cable 148, freely rotates withinself-expanding cannula 300 to maintain an appropriate pumping flowregime, e.g., from the distal side to the proximal side ofself-expanding cannula 300. FIG. 3 shows that, in some embodiments,self-expanding cannula 300 includes a cannula strut 203 that forms acage or mesh structure of filaments that extend axially alongself-expanding cannula 300 and wraps circumferentially around a centralarea of self-expanding cannula 300 in which impeller 165 of impellerassembly 116 is disposed. Cannula strut 203 can take any suitable form,such as being constructed to provide radial collapsibility andself-expandability. Self-expanding cannula 300 forms its impermissibleelongate wall structure 159 by encapsulating the middle portion ofcannula strut 203 with polymer layers so that the rotating impellertransfers the blood flow from the distal side to the proximal side ofself-expanding cannula 300 during use of the heart pump system. In someembodiments, cannula strut 203 is a metallic mesh comprising a shapememory alloy.

Catheter assembly 100 includes outer sheath assembly 121 (shown in FIG.2) configured to constrain impeller assembly 116 in a low profileconfiguration in a first state and to permit impeller assembly 116 toexpand to an enlarged configuration in a second state. Outer sheathassembly 121 has a proximal end 166, a distal end 167, and an elongatesheath body 174 extending therebetween (all shown in FIG. 2). Outersheath assembly 121 provides a passageway for inner sheath assembly 170to be sleekly disposed through outer sheath assembly 121. Thisarrangement permits inner sheath assembly 170 to be positioned betweenan advanced position corresponding to the low profile configuration ofthe heart pump and a retracted position corresponding to the enlargedconfiguration of the heart pump. In some embodiments, a luer 102 orother suitable connector is in fluid communication with proximal end166, distal end 167, and elongate sheath body 174 extending therebetweenof outer sheath assembly 121. Luer 102 can be configured to deliverfluids to catheter assembly 100, such as priming fluid, infusant, or anyother suitable fluid.

FIGS. 2 and 3 also show an atraumatic tip 182 disposed distal toself-expanding cannula 300. Atraumatic tip 182 can have an arcuateconfiguration such that interactions with a patient's internal tissuesare controlled and do not cause trauma thereto. Atraumatic tip 182 cantake any suitable shape, which can vary depending on the degree ofcurvature of the tip. The tip is designed to be atraumatic so that afterretraction of the guidewire, when the tip is left inside, for example, aventricle, it does not cause injury or trauma to the inner wall orendocardial surface of the ventricle resulting from motion of theventricle.

Atraumatic tip 182 can include a 180° bend, wherein the distal-most endof atraumatic tip 182 is generally parallel to the non-arcuate portionof atraumatic tip 182, but extending in the opposite direction (e.g., aj-tip). The distal-most end of atraumatic tip 182 can be generallyperpendicular to the non-arcuate portion of atraumatic tip 182, or at anangle between about 90° and about 180°. In yet another aspect, thedistal-most end of atraumatic tip 182 can include a 360° bend, whereinthe distal-most end of atraumatic tip 182 is generally parallel to thenon-arcuate portion of atraumatic tip 182, while extending in generallythe same direction. In some embodiments, the arcuate portion ofatraumatic tip 182 can be coiled greater than 360°.

b. Collapsible and Self-Expanding Cannula

The collapsible and self-expanding cannula of the present disclosure asdescribed herein includes open proximal end 183, open distal end 184,and an elongate fluid-impermissible wall structure, such as wallstructure 159 shown FIG. 3. Elongate fluid-impermissible wall structure159 is formed from a first balloon film having interior surface 161,cannula strut 203, and a second balloon film having exterior surface 163that are thermally fused together into an integrated hybrid cannulastructure.

Cannula strut 203 is generally formed from a shape memory alloy. In thisembodiment, cannula strut 203 includes an elongate portion that extendsfrom open proximal end 183 to open distal end 184. In one embodiment,the first balloon film disposed on an inside surface of cannula strut203 and the second balloon film is disposed on an outer surface ofcannula strut 203. Collapsible and self-expanding cannula 300 is formedin such a manner (as described in detail below) so that that the firstballoon film and the second balloon film are seamlessly integratedtogether to encapsulate cannula strut 203 and form fluid-impermissiblewall structure 159 having interior surface 161 and exterior surface 163.The first and second balloon films comprise polymeric materials and areshaped via blow molding as disclosed elsewhere herein. Elongated,fluid-impermissible wall structure 159 of cannula 300 enables thepumping functionality of a percutaneous heart pump where impeller 165 ofimpeller assembly 116 transfers the blood from open distal end 184 toopen proximal end 183 of cannula 300. The polymeric wall structure ofsuch cannula 300 has excellent surface lubricity attributes that allowfor smooth advancement and retraction of a sheath assembly and minimizesabrasive damage on rotating impeller blades in impeller assembly 116 forthe heart pump.

Referring now to FIG. 4, there is illustrated a cut away diagram ofself-expanding cannula 300 in accordance with one embodiment of thepresent disclosure. Self-expanding cannula 300 comprises elongate,fluid-impermissible wall structure 159 (shown in FIG. 2) formed bythermally integrating a first (inner) polymer balloon film 310, metalliccannula strut 203, and a second (outer) polymer balloon film 320together. First balloon film 310 is disposed on the interior surface ofmetallic cannula strut 203 to form interior surface 161 (shown in FIG.3) of self-expanding cannula 300, and second balloon film 320 isdisposed on the exterior surface of metallic cannula strut 203 to formexterior surface 163 (shown in FIG. 3) of self-expanding cannula 300.Metallic cannula strut 203 is disposed between first balloon film 310and second balloon film 320; that is, first balloon film 310 is disposedabout an interior circumference of cannula strut 203 and second balloonfilm 320 is disposed about an exterior circumference of cannula strut203. Impeller 165 (shown in FIG. 3) may be disposed within a lumen 330of self-expanding cannula 300 to pump blood from open distal end 184 toopen proximal end 183 during operation of a percutaneous heart pump whenimpeller 165 rotates at a high speed. For example, when a heart pumpcomprising self-expanding cannula 300 is collapsed to its low insertionprofile and advanced from the femoral artery into the left ventriclethrough the aortic arch of the heart, self-expanding cannula 300 isdeployed across the aortic valve and then fully expanded into theoperating configuration upon the retraction of a sheath assembly. Whenimpeller 165 spins at a high speed, the oxygen-rich blood is pulled fromopen distal end 184 of cannula 300 within the left ventricle, pumpedthrough elongate fluid-impermissible wall structure 159 of cannula 300,and sent to the ascending aorta and the body through open proximal end183 of cannula 300. Once a period of support is completed, outer sheathassembly 121 (shown in FIG. 1) is advanced to re-collapse the heart pumpsuch that cannula 300 and impeller assembly 116 are in a low profileconfiguration and can be removed from the body.

Referring now to FIG. 5, there is illustrated a cross-sectional view ofelongate, fluid-impermissible wall structure 159 of self-expandingcannula 300 of FIG. 4. As shown in FIGS. 4 and 5, interior surface 161of self-expanding cannula 300 is formed of first polymer balloon film310, and it is exposed to and may be in contact with the blades of animpeller (not shown) comprising impeller assembly. Exterior surface 163of self-expanding cannula 300 is formed of second polymer balloon film320, and is exposed to, and may be in contact with, both blood vessels(not shown) and heart tissue (not shown). Both interior surface 161 andexterior surface 163 of elongate wall structure 159 of self-expandingcannula 300 (i.e., both first balloon film 310 and second balloon film320) are exposed to, and directly in contact with, the blood.

In many embodiments of the present disclosure, cannula strut 203 ofself-expanding cannula 300 is formed from a shape memory alloy. Cannulastrut 203 is generally in the form of a braided mesh, a weaved mesh, oris laser-cut into an interconnected, maze-like pattern that allows forcollapsing and self-expanding. To make impeller assembly 116 function asa screw-type, positive displacement pump, elongate structure 159 ofcannula 300 where impeller 165 is disposed has to be fluidimpermissible. Because cannula strut 203 in the form of braided memoryshape mesh or laser-cut pattern or woven mesh is not fluid tight due toits required attributes of collapsibility or self-expanding, asillustrated in FIG. 5, the elongate portion of cannula strut 203 isencapsulated by first (or inner) polymer balloon film 310 and second (orouter) polymer balloon film 320, and thermally fused into a hybridstructure comprising fluid-impermissible, thin wall structure 159 havinginterior surface 161 and exterior surface 163 as described herein. Sucha hybrid structure of cannula 300 still exhibits comparablecollapsibility and self-expandability as an unencapsulated cannula strut(i.e., cannula strut 203 without first balloon film 310 ad secondballoon film 320). As described more fully below, first balloon film 310and second balloon film 320 desirably substantially adhere and/or fusetogether wherein they may be physically in contact each other, or bothballoon films preferably adhere to cannula strut 203 wherein firstballoon film 310 and second balloon film 320 may be physically in directcontact with cannula strut 203, and thus provide a fluid-impermissible,seamless self-expanding cannula 300 that resists delamination.

Shape memory alloys (SMA) suitable for use in construction of cannulastrut 203 are metallic alloy materials that have the ability to“memorize” or retain its previous shape when subjected to certainstimuli, such as stress or heat. An SMA material, like nitinol, may alsopossess superelasticity that allows a component comprising such amaterial to exhibit pseudo-elastic recovery or “memory” from one shapeto another multiple times upon the application and release of deformingstress or force. A small stress or force may induce considerabledeformation, but the material or component comprising such a materialrecovers its original shape when the deforming force or stress isreleased. There is no need for any other stimulus, such as heating orcooling, for the deformed material to return to its original shape. Thesuperelasticity of such an SMA material is a mechanical type of shapememory that is utilized for making cannula strut 203 exhibiting thereversible collapsing and self-expanding capacity. Under applied forceor stress, the cannula material is deformed to a lower insertionconfiguration. Because it is fabricated from an SMA, it “memorizes” itsoriginal shape and returns thereto upon the release of the deformingforce or stress.

SMAs generally display two distinct crystal forms: martensite primarilywith variant sheared platelets, and austenite (the parent or memoryphase) with long-range order. The martensite of an SMA material isself-accommodating and deforms by a so-called twining mechanism thattransforms different sheared platelet variants to the variantaccommodating to the maximum deformation in the direction of the appliedforce. At low temperatures, an SMA material may exist as martensite thatcan be deformed by a relatively small force. In contrast, at hightemperatures, the material may exist as austenite which is hard todeform like normal metals. Therefore, upon thermal stimulus (heating orcooling), an SMA material may undergo phase transformation astemperature increases or decreases. For example, when heated, an SMAmaterial that exists as martensite (e.g., ambient or body temperature)may start to undergo the phase transformation-to-austenite at aso-called “Austenite-Start temperature” (A_(s) or A₂) and finish thetransformation at a relatively high, so-called “Austenite-Finishtemperature” (A_(f) or A₁), above which the material exists as austenite(i.e., the parent or memory phase), displaying shape memory. Similarly,upon cooling, an SMA material that exists as austenite may start toundertake the transformation-to-martensite at a so-called“Martensite-Start temperature” (M_(s) or M₂) and finish thetransformation at a relatively lower so-called “Martensite-Finishtemperature” (M_(f) or M₁), below which the material exists asmartensite, exhibiting shape recovery. Such phase transformationsinduced by thermal stimulus is illustrated in FIG. 10. Due to materialhysteresis, phase transformation temperatures at which an SMA materialmay exist at a similar or comparable phase are not equal. For example,M_(s) and A_(f) (or M_(f) and A_(s)) at which a SMA material exists insimilar phases are not equal. In general, an “Austenite-Finishtemperature (A_(f)) is utilized to characterize the shape memory andhyperelasticity effects of an SMA material.

In addition to thermal stimulus, phase transformation-to-martensite orphase transformation-to-austenite of an SMA material may take placeunder other stimulus, such as applied force or stress. For example, foran SMA material that exists as austenite at the temperature of interestthat is slightly below its active “Austenite-Finish temperature” A_(f)(or comparably “Martensite-Start temperature” M_(s)), applied stress may“force” the material to undergo the phase transformation-to-martensite,at which the material would exhibit considerable deformation for arelatively small applied force or stress. Once the force or stress isreleased, the material in martensite reverts back to austenite andrecovers its original shape (the memory phase). Such phasetransformation-to-martensite effect as induced by external force orstress makes an SMA material appears to be extremely elastic, and isknown as superelasticity. This superelasticity is used for the selectionof SMA materials for fabricating the cannula strut herein.

Examples of SMA materials include, but are not limited to,nickel-titanium (nitinol), copper-zinc, copper-zinc-aluminum,copper-aluminum-nickel, and gold-cadmium. Desirably, the shape memoryalloy is nickel-titanium (nitinol). For a typical SMA material, itsactive A_(f) varies based on the exact composition of the material. Insome embodiments, cannula strut 203 comprises a shape memory alloyhaving an active austenite finish temperature (A_(f)) that is near orbelow the body temperature of the patient. In humans, that temperatureis generally about 98.6° F. or 37° C. In some aspects, the A_(f) of theshape memory alloy is from 0° C. and 35° C. In yet another aspect, theA_(f) is from 5° C. to 30° C. In yet another aspect, the A_(f) is from10° C. to 25° C. In still yet another aspect, the A_(f) is from 10° C.to 20° C. In some embodiments, cannula strut 203 comprises nitinol.

Self-expanding cannula 300 as described herein further comprises firstballoon film 310 and second balloon film 320 as noted above. In someembodiments, one or both of the balloon films comprise a plurality oflayers (see FIG. 6, for example). In some embodiments, one or both ofthe balloon films comprise two layers. In other embodiments, one or bothof the balloon films comprise three layers. In still other embodiments,one or both of the balloon films comprise more than three layers. Eachlayer of first balloon film 310 or second balloon film 320 may be thesame or different from any other layer. For first balloon film 310having a plurality of layers, its surface layer defines interior surface161 of cannula 300 that is exposed, or adjacent, to the impeller blade,with a minimal clearance. For second balloon film 320 having a pluralityof layers, its surface layer defines exterior surface 163 of cannula 300that is exposed to the surface of the blood vessels and the center lumenof outer sheath assembly 121. Interior surface 161 and exterior surface163 will be directly exposed to the blood. In all aspects, thecircumference of exterior surface 163 is larger than the circumferenceof the interior surface 161.

The distance between interior surface 161 and exterior surface 163defines the total thickness of elongate, fluid-impermissible wallstructure 159 that comprises cannula 300. In some aspects the thicknessof the cannula wall is from 25 μm to 250 μm. In yet another aspect, thethickness of the cannula wall is from 50 μm to 150 μm. In still yetanother aspect, the thickness of the cannula wall is about 50 μm, about75 μm, about 100 μm, about 125 μm, about 150 μm, about 175 μm, about 200μm, about 225 μm, or about 250 μm.

The thickness of elongate, fluid-impermissible wall structure 159 ofcannula 300 is determined by the thickness of first balloon film 310,the thickness of second balloon film 320, and the thickness of cannulastrut 203. In some aspects the thickness of first balloon film 310 andsecond balloon film 320 is each independently from 10 μm to 200 μmthick. In some aspects, the thickness of each film is about 10 μm, about20 μm, about 30 μm, about 40 μm, about 50 μm, about 60 μm, about 70 μm,about 80 μm, about 90 μm, about 100 μm, about 110 μm, about 120 μm,about 130 μm, about 140 μm, about 150 μm, about 160 μm, about 170 μm,about 180 μm, about 190 μm, or about 200 μm.

Referring now to FIG. 6A, there is illustrated a balloon film 500including a first layer 502 and a second layer 504 such that balloonfilm 500 includes two layers. Second layer 504 is in contact with shapememory alloy 506 (i.e., cannula strut 203) and second layer 504 is alsoin contact with first layer 502. Referring now to FIG. 6B, there isillustrated a balloon film 508 including a first layer 510, a secondlayer 512, and a third layer 514 such that balloon film 508 includesthree layers. Second layer 512 is sandwiched between first layer 510 andthird layer 514 and third layer 514 is in contact with shape memoryalloy 516 (i.e., cannula strut 203). Referring now to FIG. 6C, there isillustrated a shape memory alloy 518 (i.e., cannula strut 203) beingencapsulated by a first balloon film 520 and a second balloon film 521.First balloon film 520 includes a first layer 522, a second layer 524,and a third layer 526. Second balloon film 521 includes a first layer528, a second layer 530, and a third layer 532.

As noted above, one or both of first balloon film 310 and second balloonfilm 320 may include one, two, three or more layers. In manyembodiments, one or more layers are desirably biocompatible, andgenerally include a biocompatible polymer. In some aspects the polymeris a biocompatible thermoplastic elastomer. Each layer of first balloonfilm 310 and second balloon film 320 may be the same or different. Insome embodiments, each biocompatible thermoplastic elastomer isindependently selected from the group consisting of a polyurethane blockcopolymer having both hard blocks and soft blocks, a poly(ether amide)block copolymer, a poly(ether ester) block copolymer, a functionalizedpolyolefin polymer (olefinic) or copolymer grafted with polar functionalgroups, a functionalized polystyrene (styrenic) copolymer grafted withpolar functional groups and combinations thereof. In some embodiments,the biocompatible thermoplastic elastomer comprises a polyolefin polymer(olefinic) or copolymer grafted with polar functional groups and/or apolystyrene (styrenic) copolymer grafted with polar functional groupswhere the polar functional groups are selected from the group consistingof maleic anhydride, acrylate, epoxy, amine, and combinations thereof.Desirably, in many embodiments, the biocompatible thermoplasticelastomer for the first balloon film, the second balloon film or both isa thermoplastic polyurethane material.

In another embodiment, the biocompatible thermoplastic elastomer isselected from the group of segmented polyurethane block copolymers thatcomprises the hard urethane segment/block chemically derived from anaromatic or aliphatic diisocyanate and a diol or diamine chain extenderand the soft segment/block chemically derived from one or morepolyglycol(s) such as polyester glycol(s), polyether glycol(s),polycarbonate glycol(s), dihydroxylated silicone polymer(s) and anycombinations thereof. For example, commercially available Tecoflex™thermoplastic polyurethane resins comprises a family of aliphaticpoly(ether urethane) block copolymers whose hard block is chemicallyderived from 4,4′-methylenebis(cyclohexyl isocyanate) and 1,4-butanediol, and soft blocks from polyether glycol (poly(tetramethylene oxide)glycol). For another example, commercially available Elast-Eon™ orPursil® thermoplastic polyurethane resins comprise a family ofsilicone-poly(ether urethane) copolymers whose hard blocks arechemically derived from an aromatic isocyanate (i.e. methylene diphenyldiisocyanate) and 1,4-butane diol, soft blocks from two differentpolyglycols, including a dihydroxylated polydimethylsiloxane polymer anda polyether glycol. For yet another example, commercially availablePellethane® or Elasthane™ thermoplastic polyurethane resins comprise afamily of poly(ether urethane) copolymers whose hard blocks arechemically derived from an aromatic isocyanate (i.e. methylene diphenyldiisocyanate) and 1,4-butane diol and soft blocks from polyether glycol(i.e. poly(tetramethylene oxide) glycol). For a first or second balloonfilm, each comprising only one layer, a biocompatible thermoplasticpolyurethane resin is preferably used as the balloon material. Such apolymer may be selected from the group comprising poly(ether-urethane)resin family (Elasthane™, Pellethane®, and the like), orsilicone-poly(ether-urethane) resin family (Pursil®-ElastEon®, and thelike), or poly(carbonate-urethane) resin family (Bionate® and the like),or silicone-poly(carbonate-urethane) resin family (Carbosil® and thelike), or combinations thereof.

In some embodiments, a polymer blend or admixture comprising two or morethermoplastic polyurethane resin material(s) having different hard-blockand/or soft-block types may be used for one or both of first balloonfilm 310 or second balloon film 320 that comprises only one layer. Forexample, a poly(ether urethane) block polymer resin can be blended oradmixed with a silicone-poly(ether urethane) block copolymer and used asa balloon material for first balloon film 310 and/or second balloon film320.

In yet another aspect, first balloon film 310 or second balloon film 320may comprise two or more layers. The top layers of the balloon films maycomprise a nonpolar olefinic thermoplastic elastomer having good surfacelubricity.

In some aspects where first balloon film 310, second balloon film 320,or both comprise three layers, the intermediate layer (that is, thelayer between the inner and outer layers) comprises a polymer that isadhesive and will facilitate attachment of the other two layers. Someadhesive polymers have linking or coupling functional groups including,but not limited to, maleic anhydride, acrylic monomers, epoxy and aminegroups.

In still yet another aspect, first balloon film 310 and/or secondballoon film 320 may comprise two or more film layers. The top layers ofthe balloon films may be selected from fluorinated thermoplasticelastomer polymers. Examples of fluorinated elastomer polymers include,but are not limited to, fluorinated ethylene-propylene copolymer,perfluoroalkoxy alkane polymer, and the like. These polymers may be usedindividually or incorporated as a polymer blend with any other polymerdisclosed herein.

c. Manufacturing the Collapsible and Self-Expanding Cannula

Also disclosed herein are methods for manufacturing collapsible andself-expandable cannula 300 as described herein for use with apercutaneous heart pump or other medical device. Fabrication of cannula300 may be done using a two-step process in many embodiments. In thefirst step, first balloon film 310 and second balloon film 320 areprepared using a suitable blow molding process. In the second step, theprepared first balloon film 310 and second balloon film 320 areassembled with cannula strut 203 (generally constructed from an SMA) andintegrated into a hybrid structure from the inward radial pressure of ashrink tube used in the manufacturing process as described herein.

In many embodiments, first balloon film 310 and/or second balloon 320film are prepared from a polymer parison 710 using a blow molding device700 (See FIGS. 9A and 9B). Polymer parison 710 comprises an extrudedtube from any polymer or a coextruded tube from any combination ofpolymers as disclosed elsewhere herein. Polymer parison 710 isintroduced onto a blowing mandrel 718 and tightly sealed at its ends bythe mold's seal plates 716. Blowing mandrel 718 affixed on movingcartridge 712 moves into and resides inside the cavity of blow mold 704.After closing, the mold and the polymer tube are heated inside blow mold704 by thermal module 702. A pressurized blowing gas 708 is introducedfrom the mandrel's gas inlet such that heated polymer parison 710 isblown into a balloon film adapted to the cavity of the mold. After theblow mold 704 is cooled by the thermal module, the blown balloon film isreleased from the mold and the blowing mandrel 718 and trimmed formaking cannula 300. Both first balloon film 310 and second balloon canbe prepared in this manner in preparation for fabricatingself-expandable and collapsible cannula 300 for a percutaneous heartpump. Other suitable balloon film preparation processes are also withinthe scope of the present disclosure.

Also disclosed herein is a specific method for forming and manufacturingcollapsible and self-expanding cannula 300 that comprises a firstballoon film 602 that defines first balloon film 310 (shown in FIG. 5),cannula strut 203, and a second balloon film 604 that defines secondballoon film 320 (shown in FIG. 5). FIGS. 7A and 7B are a flow diagramillustrating such a method 400, and FIGS. 8A-8E are schematic diagramsillustrating performance of method 400.

Referring now to FIGS. 7A and 7B, in one embodiment, method 400comprises introducing 402 first balloon film 602 onto a supportingmandrel 600; expanding 404 cannula strut 203; introducing 406 expandedcannula strut 203 onto supporting mandrel 600 such that cannula strut203 contacts and fits against first balloon film 602; introducing 408second balloon film 604 onto supporting mandrel 600 such that secondballoon film 604 contacts and fits against cannula strut 203;introducing 410 a shrink tube 606 onto supporting mandrel 600 such thatshrink tube 606 contacts and fits against second balloon film 604 andwraps around the outer surface of second balloon film 604 therebycreating a balloon-strut-balloon assembly; heating 412 theballoon-strut-balloon assembly so that at least one of first balloonfilm 602 and second balloon film 604 at least partially melts and atleast partially adheres to cannula strut 203 such that spaces within theballoon-strut-balloon assembly are filled up by polymer melt under aninward radial pressure exerted by shrink tube 606 thereby creating afused hybrid balloon film; and removing 414 shrink tube 606. It isunderstood that numerous modifications can be made to this method andthat other arrangements can be devised without departing from the spiritand scope thereof. As one non-limiting example, in some embodiments,cooling of the final fused balloon film is done before removing shrinktube 606. In yet another embodiment, cooling of the final fused balloonfilm is done after removing shrink tube 606.

Referring generally now to FIGS. 8A-8E and in further reference toforming and manufacturing collapsible and self-expanding cannula 300that comprises first balloon film 602 that defines first balloon film310 (shown in FIG. 5) and second balloon film 604 that defines secondballoon film 320, FIG. 8A illustrates empty supporting mandrel 600 forforming collapsible and self-expanding cannula 300 having an elongatefluid-impermissible wall structure 159 extending from open proximal end183 to open distal end 184 of cannula 300. FIG. 8B shows first balloonfilm 602 introduced onto the outer profile surface of supporting mandrel600 after being trimmed, inserted and properly positioned. FIG. 8C showscannula strut 203 being introduced onto and against first balloon film602 that is properly situated on supporting mandrel 600. Cannula strut203 is expanded before being placed onto supporting mandrel 600. FIG. 8Dshows second balloon film 604 introduced overtop of cannula strut 203such that all three components of this embodiment: first balloon film602, cannula strut 203 and second balloon film 604, are all properlysituated on supporting mandrel 600 thereby forming a hybridballoon-strut-balloon assembly. FIG. 8E shows shrink tube 606 beingintroduced to fully wrap around and encapsulate theballoon-strut-balloon assembly, including open proximal end 183 and opendistal end 184. FIG. 8E further illustrates the application of an inwardradial pressure in conjunction with heat on shrink tube 606 to atemperature at which first balloon film 602 and/or second balloon film604 at least partially melts to fill any gaps or spaces within theballoon-strut-balloon assembly. The pressure of shrink tube 606 inconjunction with heat forces first balloon film 602 and/or secondballoon film 604 to encapsulate and adhere to the surface of cannulastrut 203.

Heat to the balloon-strut-balloon assembly (including shrink tube 606)can be supplied from any convenient source (not shown in the Figures),including, but not limited to, an oven, a vacuum oven, an inductionheater, an RF heater, an IR heater, and the like. When first balloonfilm 602 and/or second balloon film 604 are heated above their meltingor glass transition temperatures, they will at least partially (and inmany embodiments, completely) melt and begin to flow. The first balloonfilm 602 and second balloon film 604, under radial, compressive pressurefrom shrink tube 606, will flow through the structural spaces of cannulastrut 203 such that first balloon film 602 and second balloon film 604contact one another and at least partially (and in many embodiments,completely) flow together. This creates an integrated structure betweenfirst balloon film 602 and second balloon film 604 such that theboundary or surface of each balloon film is not clearly delineated. Thisintegration of first balloon film 602 and second balloon film 604greatly reduces or even eliminates delamination of elongated, fluidimpermissible wall structure 159 of self-expanding cannula 300 duringoperation of the percutaneous heart pump.

After fusing together as one hybrid entity, the thermally-integratedballoon-strut-balloon assembly may be naturally or forcibly cooled.After the desired cooling, shrink tube 606 is then removed. Even withouttrimming, the resultant assembly comprises finished cannula 300 havingelongated fluid-impermissible wall structure 159 with an internalprofile surface conforming to the external profile surface of supportingmandrel 600, open proximal end 183, and open distal end 184 (shown inFIGS. 2 and 3). It is understood that first balloon film 602 and secondballoon film 604 may comprise a plurality of layers as discussed hereinand previously illustrated in FIGS. 6A, 6B and 6C. All three componentsin such a hybrid cannula are thermally fused together before the shrinktube 606 is removed. By properly selecting a combination of differentpolymer materials for each layer of the first balloon film 602 and/orsecond balloon film 604 as disclosed elsewhere herein, elongatefluid-impermissible wall structure 159 of cannula 300 will exhibitstrong adherence from one layer to another and between catheter strut203 and the layers with which catheter strut 203 is in direct contact.Additionally, such an elongated wall structure 159 has minimal or noimpact on the collapsibility and self-expanding of “bare” cannula strut203. Furthermore, delamination between any balloon film layers and fromthe metallic surfaces of cannula strut 203 is eliminated.

In some desirable embodiments, the ends of the thermally-integratedfirst and second balloon films are trimmed such that afluid-impermissible elongate wall structure 159 comprising the cannulais at least as long as an impeller 165 (see FIG. 3) of the percutaneousheart pump and slightly longer than the maximum thickness of the aorticvalve of a typical patient.

In many embodiments of the illustrated method, shrink tube 606 exerts aninward radial pressure on first balloon film 602, cannula strut 203 andsecond balloon film 604 upon heating the assembly as shown in FIG. 8E.The thickness of the newly formed elongate fluid-impermissible wall canbe of any desired thickness, as noted above. Heating theballoon-strut-balloon assembly fuses first balloon film 602 and secondballoon film 604 onto cannula strut 203 and onto each other in order tomake a fully integrated and continuous surface and fluid-impermissiblewall of the self-expanding cannula. In many embodiments, the polymer orpolymers selected for each of the layers of first balloon film 602 andsecond balloon film 604 are desirably selected such that, when melted,they readily fuse and integrate together. The temperature to which theballoon-strut-balloon assembly is heated will vary based on the criticalthermal transition temperatures, namely the melting temperatures forsemicrystalline polymers or glass transition temperatures for amorphouspolymers that comprise first balloon film 602 and second balloon film604. In some embodiments, the heating is above 50° C., above 75° C.,above 100° C., above 125° C., above 150° C., above 175° C. or above 200°C. Desirably, the temperature is between 100° C. and 250° C.

Because shrink tube 606 is removed from the self-expanding cannula afterits manufacture, shrink tube 606 is generally formed from a materialthat is stable to the temperatures achieved in the manufacturing processand does not stick/adhere to the surface (outer) layer of second balloonfilm 604 to which it contacts to provide the above-described pressure.Desirably, in many embodiments shrink tube 606 is a fluorinated polymeror a fluoropolymer, such as polytetrafluoroethylene, perfluoroalkoxypolymer, fluorinated ethylene-propylene copolymer,ethylene-teterfluoroethylene copolymer or the like that is highlyresistant to polymer adhesion.

Although the embodiments and examples disclosed herein have beendescribed with reference to particular embodiments, it is to beunderstood that these embodiments and examples are merely illustrativeof the principles and applications of the present disclosure. It istherefore to be understood that numerous modifications can be made tothe illustrative embodiments and examples and that other arrangementscan be devised without departing from the spirit and scope of thepresent disclosure as defined by the claims. Thus, it is intended thatthe present application cover the modifications and variations of theseembodiments and their equivalents.

This written description uses examples to disclose the subject matterherein, including the best mode, and also to enable any person skilledin the art to practice the disclosure, including making and using anydevices or systems and performing any incorporated methods. Thepatentable scope of the disclosure is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

What is claimed is:
 1. An expandable cannula for a percutaneous heartpump, the expandable cannula comprising: a substantially open proximalend; a substantially open distal end; and an elongate central portiondisposed between the proximal end and the distal end, the elongatecentral portion having an inner surface and an opposing outer surface; afirst fluid impermeable film disposed on at least one of the innersurface and the outer surface, the first fluid impermeable filmcomprising a polymer and having a thickness within a range of from 10 μmto 200 μm.
 2. The expandable cannula according to claim 1, wherein thefirst fluid impermeable film is disposed on the first surface and asecond fluid impermeable film is disposed on the second surface.
 3. Theexpandable cannula according to claim 2, wherein the second fluidimpermeable film comprises a polymer and has a thickness within a rangeof from 10 to 200 μm.
 4. The expandable cannula according to claim 1,wherein the elongate central portion of the cannula comprises a shapememory alloy.
 5. The expandable cannula according to claim 1, whereinthe first fluid impermeable film is a laminate comprising at least twolayers.
 6. The expandable cannula according to claim 1, wherein thefirst fluid impermeable layer is thermally bonded to the elongatecentral portion.
 7. The expandable cannula according to claim 1, whereinthe elongate central portion comprises a mesh structure.
 8. Theexpandable cannula according to claim 7, wherein the first fluidimpermeable film is disposed on the first surface and a second fluidimpermeable film is disposed on the second surface, and the first fluidimpermeable film is bonded to the second fluid impermeable film via bondstructures extending through the mesh structure.
 9. The expandablecannula according to claim 8, wherein the first fluid impermeable filmand the second impermeable film are thermally bonded to one another. 10.The expandable cannula according to claim 8, wherein a total wallthickness of the first fluid impermeable film, the elongate centralportion and the second fluid impermeable film together is from 70 μm to550 μm.
 11. The expandable cannula according to claim 8, wherein each ofthe first fluid impermeable film and the second fluid impermeable filmcomprise a plurality of layers.
 12. The expandable cannula according toclaim 8, wherein at least one of the first fluid impermeable film andthe second fluid impermeable film comprises a biocompatible polymer. 13.The collapsible cannula according to claim 1, wherein the thermaltransition temperature of the polymer is from 50° C. to 250° C.
 14. Thecollapsible cannula according to claim 13, wherein the thermaltransition temperature is from 100° C. to 250° C.
 15. The expandablecannula according to claim 1, wherein the elongate central portioncomprises a nickel-titanium alloy.
 16. The expandable cannula accordingto claim 1, wherein the polymer is a thermoplastic elastomer.
 17. Theexpandable cannula according to claim 16, wherein the thermoplasticelastomer is selected from the group consisting of a thermoplastic,segmented polyurethane block copolymer, a poly(ether-b-amide) copolymer,poly(ether ester) block copolymer, a functionalized olefinicthermoplastic elastomer having polar functional groups, a styrenicthermoplastic elastomer functionalized by polar functional groups, andcombinations thereof, wherein the polar functional groups are selectedfrom the group consisting of maleic anhydride, acrylate, epoxy, amine,and combinations thereof.
 18. The expandable cannula according to claim1, wherein the first fluid impermeable film is disposed on the firstsurface and a second fluid impermeable film is disposed on the secondsurface and wherein the first fluid impermeable film, the second fluidimpermeable film, and the elongated central portion are a fusedintegrated structure having a substantially smooth, continuous innersurface and a substantially smooth, continuous outer surface.
 19. Thecollapsible and self-expanding cannula according to claim 18, wherein asurface layer of the first fluid impermeable film comprises a firstbiocompatible thermoplastic elastomer, and a surface layer of the secondfluid impermeable film comprises a second biocompatible thermoplasticelastomer.
 20. The collapsible and self-expanding cannula according toclaim 19, wherein the first biocompatible thermoplastic elastomer andthe second biocompatible thermoplastic elastomer, are independentlyselected from the group consisting of a thermoplastic polyurethane blockcopolymers comprising hard blocks and soft blocks of different types,and wherein the hard blocks and the soft blocks are selected from thegroup consisting of poly(ether urethane), poly(carbonate urethane),poly(ester urethane), silicone-poly(ether urethane),silicone-poly(carbonate urethane), and a blend or admixture of acombination thereof.